andLinux.org is a complete Ubuntu Linux system running seamlessly in Windows 2000 based systems (2000, XP, 2003, Vista [32-bit only]). This project was started for Dynamism for the GP2X community, but its userbase far exceeds its original design. andLinux is free and will remain so, but donations are greatly needed.
andLinux uses CoLinux as its core which is confusing for many people. CoLinux is a port of the Linux kernel to Windows.